Snowy Range Instruments

Transcription

1 Snowy Range Instruments

2 Cary W Hg Arc JY U W Ar + Laser DL Solution mw SnRI CBEx mw

3 What is Raman Spectroscopy? Raman spectroscopy is a form of molecular spectroscopy. It is the inelastically scattered light from molecular vibrations. Advantages of Raman Spectroscopy Little to No Sample Preparation Required Performs Analysis Directly Through Transparent Containers (i.e. plastic bags, glass, etc.) Permits Both Qualitative and Quantitative Analysis Highly Selective Fast Analysis Times Insensitive to Aqueous Vibrational Bands 1/19/2015

4 Electron state explanation of Raman Optical Field Incident on a Molecule o (cm -1 ) o - Stokes Inelastic Scattering Elastic Scattering o Rayleigh o + Anti-Stokes v = 2 v = 1 v = 0 Electronic Excited States Virtual Excited States Vibrational Levels

5 Wave Raman H O H Electromagnetic radiation has an electric field associated with it. The electric field of the radiation can interact with the molecules in the sample through the POLARIZABILITY of the molecules. Polarizability is related to the ability electronic cloud surrounding the molecule to interact with the an electric field. Soft molecules like benzene tend to be very strong Raman scatterers. Hard molecules like water tend to be very poor Raman scatterers. The wave concept of Raman scattering is conceptually equivalent to FM radio. The laser operates at the carrier frequency (105.5 FM) and the vibrations are the side bands (Music). 1/19/2015

6 Particle Raman H O H Electromagnetic radiation can be thought of as being composed of particles (photons). The photons sometimes hit a molecule and bounce off. If the collision is inelastic and energy is lost by making the molecule vibrate, the photon will have less energy. The number of photons scattered is related to the electronic size of the molecule. Large pi bonds, like those in benzene, will scatter more than small sigma bonds in water. The temperature dependence of Raman scattering follows Boltzmann s Law and can only be explained by the particle or quantum concept of Raman scattering. 1/19/2015

7 The Virtual State Virtual: being such in essence or effect though not formally recognized or admitted. Merriam-Webster Dictionary the energy of the molecule can assume any of an infinite number of virtual states between the ground state and the first electronic state Skoog, Holler, and Nieman Heisenberg: The uncertainty in the energy of a state is inversely related to the lifetime of the state. The lifetime of a scattering process is infinitely short, so the breadth of the energy state is infinitely broad. This is the virtual state of Raman scattering. 1/19/2015

8 Raman Spectroscopy Raman Activity Requirement (Selection Rule) h O C O C For Raman effect to occur the molecule must go through a polarization induced by the electric component of the electromagnetic wave O O Polarization is ease of distortion of a chemical bond 1/19/2015

9 Effect of bond strength (K) As K ν (CC) Aliphatic Ring (CC) Aromatic Ring m K C=C 1/19/2015

10 Effect of mass (µ) As µ ν C-C C-H (CH 3 ) 2 C=O C=O CH 3 C-O CH 2 CH 3 CH 2 OH CH 3 S=O (CH 3 ) 2 S=O CH 3 CH 2 O 2 CCH 3 C=O Aromatic C 6 H 5 CH 3 CH 3 Aromatic-H Raman Shift (cm -1 ) 1/19/2015

11 Raman Instrumentation The components of a Raman spectrometer 1/19/2015

12 Raman Instrumentation Raman s Discovery The Early Years Arc Lamp 90 Degree Scattering Big Spectrograph Photographic Plate 1/19/2015

13 Basic Components of a Raman System Long Pass Filter Grating CCD Laser Benzene Raman Laser Light Raman Computer Processing Intensity Wavenumber (cm-1) 1/19/2015

14 Frequency Calibration TiO 2 Calibration Acrylic Calibration Standard Must have peaks through the range Raman is relative to the laser line, the standard should be a Raman material TiO wavenumbers Acrylic 1/19/2015

15 Enhancing Raman Signal Making a better Raman Spectrum 1/19/2015

16 Integration Time As the integration increases the SNR ratio increases Example o 0.1 sec vs. 2.5 sec Much clearer, well defined peaks. Raman has clear easy to distinguish peaks

17 Interferences in Raman Raman scattering is an inherently weak process Fluorescence The largest, most common interference of Raman Molecule excited to electronic state, through radiationless transition the molecule decays to a lower energy level From the lower level the molecule can decay to the ground state while emitting radiation which interferes with Raman Avoid colored samples Ambient Light and Background Caused by overhead light in the lab or sunlight Corrected with auto reference on the system Thermal effects Burning the sample- ORS helps greatly with this Absorption Very minimal

18 Orbital Raster Scanning The solution to an age old issue with Raman

19 Instruments Orbital Raster Scan (ORS ) Competitor Raman systems have difficulty with heterogeneous samples, such as pharmaceuticals, and with materials that are photo/heat sensitive. Conventional Raman uses a small spot-size for optimal spectral resolution. Increasing the spot-size captures more materials, but lowers the spectral resolution. ORS maintains the small spot-size, high resolution, and captures more materials.

20 ORS Heterogeneous sample

21 Benefits of ORS The leading advantage over all other Raman systems Large surface coverage o o Reproducibility Mixtures Thermal degradation minimized o Decreased risk of burning or damaging samples November 25, 2014

22 Example: Chemical Mixtures Pharmaceuticals are a combination of excipients and active pharmaceutical ingredients (API) mixed into a carefully controlled final formulation. Effervescent cold medicine is one example of a formulation containing three different APIs; aspirin (pain relief), chlorpheniramine maleate (antihistamine), and phenylephrine bitartrate (decongestant). The formulation of the tablets results in a homogeneous distribution of the APIs.

23 ORS Data collection ORS Off ORS On

24 ORS Matching Table 1.1 Matching- Correlation Scores Sample Matching ORS ON Matching ORS OFF Sample Sample Sample Less confident and inconsistent matching without ORS

25 ORS Spectra All twenty ORS Off spectra were averaged together and matched to one ORS on scan.

26 CBEx

27 Sampling Capabilities: collected samples in vials CBEx is designed for Class 1 laser safe identification of materials Materials can be placed in a vial for on-site identification and stored for validation Our sealed/interlocked cover allows laser safe operation Vial Well Unknown Material 2 AA Batteries Sealed/Laser Safe Operation

28 Sampling Capabilities: detecting insidious materials CBEx is designed for point and shoot operation Materials can be measured on-site through thick glass containers CBEx has an adjustable tip for easy contact measurements in bottles or white powders. Adjustable point and shoot tip Identification of material in an unlabeled bottle

29 Rapid Acquisition: confident identification CBEx has an internal calibration for maximum confidence CBEx performs rapid measurements in < 3 seconds CBEx provides a visual confirmation between library and sample and provides a confidence level Internal calibration Rapid Acquisition Confident Identification